1. Field of the Invention
The present invention relates to a coil component and a magnetic metal powder containing resin used therefor, and particularly relates to a composition of a magnetic metal powder containing resin that constitutes a magnetic path of a coil.
2. Description of Related Art
In the field of commercial or industrial electronic devices, a surface-mount coil component is frequently used as a power inductor. This is because the surface-mount coil component is small-sized, thin, and excellent in its electrical insulation property, and can be manufactured at a low cost.
As one of specific structures of the surface-mount coil component, there is a planar coil structure to which a printed circuit board technique is applied. This structure is briefly explained from the viewpoint of manufacturing processes. First, seed layers (base films) of a planar spiral shape are formed on a printed circuit board. The printed circuit board is immersed in a plating solution and a DC current (“plating current”) is carried through the seed layers, thereby electrodepositing metal ions in the plating solution onto the seed layers. Accordingly, planar spiral conductors are formed. Thereafter, an insulating resin layer covering each of the formed planar spiral conductors, a protection layer, and a magnetic metal powder containing resin layer serving as a magnetic path are sequentially formed, thereby completing a coil component. This structure can keep the size and position accuracy very high and make the coil component small-sized and thin. Japanese Patent Application Laid-open No. 2006-66830 discloses a planar coil element having such a planar coil structure.
One of the methods of increasing the coil inductance is a method of improving the magnetic permeability of a magnetic path. To improve the magnetic permeability of the magnetic path in the coil component mentioned above, it is necessary to increase the packing fraction of metal powder in the magnetic metal powder containing resin. To increase the packing fraction of the metal powder, it is effective to fill the gaps of metal powder having a large grain diameter with metal powder having a small grain diameter. However, if packing becomes closer and the metal powder excessively contacts another metal powder, there is a problem that a core loss increases and DC superposition characteristics are degraded.